Electrical gaseous discharge device



Jan.14, 1941. i 1 D LE VAN 2,228,276 'ELECTRICAL GAsEous DISCHARGEDEVICE- original Filed April' 1o. i957 J 7106275021 JAMES D Le VAN 8%@Patented Jan. 14, 1941 PATENT OFFICE ELECTRICAL GASEOUS DISCHARGE DEVICEJames D. Le Van, Belmont, Mass., assigner, by .mesne assignments, toRaytheon Manufacturing Company, a `corporation of Delaware ApplicationApril 10, 1937, Serial No. 136,159 Renewed May 11, 1940 13 Claims.

`Thisinvention relates to gaseous disch'arg tubes and to systemsutilizing the same. One of the objects of the invention is to produce anelectrical discharge between two elecz trodes in an ionizable gas withvery low voltage drop or even zero voltage drop.

Another object is to increase the efficiency of gaseous discharge tubes,particularly those in which an ionized gaseous discharge serves as asource of current carriers for a controlled space discharge.

The foregoing and other objects of my invention will 'be best understoodfrom the following description of exemplications thereof, reference tbeing had to the accompanying diagrammatic V2 preferably of glass,having a reentrant stem 2,

the upper end of which carries a press 3 in which are sealeda number oflead-in electrode supporting wires. Above the press and within theenvelope I are supported a number of electrodes. One of these electrodesconsists of a cathode 4. This cathode is of the usual type ofindirectlyheated cathode ordinarily used in Vacuum tubes, and consistsof a hollow metal cylinder 5 coated on the exterior thereof withelectron-emitting material I, such as, for example, the oxides of alkaliearth metals. The coating is heated to thermionic emission by means 0fan internal heater consisting usually of a coil of ne wire. The two endsof the heating filament I' and 8 '440 are connected to the two wires 9'land III sealed in the press 3. Surrounding the cathode 4 is theso-called cathanode 'I'. This cathanode consists of an extendedelectrode having perforations over its surface, and preferably is in theform of a '54 nne wire grid. Surrounding the cathanod'e 'l 50 form of ane wire grid. Surrounding all of the other electrodes and substantiallyconcentric therewith is the anode 9 which is preferably formedA of athin solid metal plate. The -cathanOde is preferably supported inposition by means of supporting standards II and I2. Two

`lead-in wires 9 and Ill, respectively. An exn (Cl. Z50-36) plates I3and I4 close the upper and lower open ends of the cylindrical cathanodel. The plates I3 and I4 have an opening I5 in the center thereof throughwhich the cathode 4 passes freely. The cathode 4 is supported from thetwo plates I3 and I4 by means of insulators IB and I1. The controlelectrode 8 is supported by supporting standards I8 and I 9 while theanode 9 is supported from a supporting standard by having a radialmember 2| extending from said 10 anode 9 and engaging said supportingstandard 2U. All of said electrodes are maintained in a definiterelative position by the two insulating plates 22 and 23, which havesmall openings which receive the upper and lower ends respectively ofthe various supporting standards. External connections to the heatingfilament are made through wires 24 and 25 connected to the ternalconnection is made to the cathode 4 by means of a cathode leadk 26welded to the lead-in wire 2l to which an external conductor 28 isconnected. The supporting standard I2 for the cathanode 'I has its lowerend sealed in the press 3, and has an external conductor 29 connected ithereto, thereby establishing an external connection to said cathanode.The supporting standard 20 for the anode 9 also has its lower end sealedin the press 3, and an external conn ductor 30 connected theretoestablishes an external connection for said anode. An additionalsupporting standard 3| whose lower end is sealed in the press 3 passesthrough openings in the upper and lower insulating members 22 and 23,respectively, and serves as an additional support for the electrodestructure. The lower end of the supporting standard I9 of the controlelectrode 8 is welded to the supporting standard 3I. An externalconductor 32 connected thereto establishes an external connection to thecontrol A0 element 8. The envelope I is evacuated in accordance with theusual vacuum technique. After the tube has been evacuated, it is lledwith a gas filling, such as helium or mercury vapor. The gas pressure ofthe lling may vary over a relatively wide range. However, this gaspressure is sufficiently high so that ionization can be produced thereinto the degree as will be described below. When a vapor is used, such asmercury vapor, a quantity of mercury 33 is 5.0 introduced into the tube.I have operated tubes in accordance with this invention at mercury vaporpressures of the order of ten microns and noble gas pressures of theorder of 100 to 300 microns. It is to be understood that any gaspressure which will produce the results herein described could be used.

The tube as described above may be made to operate substantially inaccordance with the principles as set forth in my patent, No. 1,962,159,granted June 12, 1934. By initially establishing a discharge between thecathode 4 and the cathanode 1, the gas in the space between said twoelectrodes is ionized. A large number of the electrons which pass intothe gaseous discharge space between the cathode and the cathanode tube,the distance between the opposing electrode surfaces is of the order ofmagnitude of the mean free path of the molecules in the gas. Due to thisspacing, a comparatively large voltage can be impressed across theseelectrodes without producing a self-sustaining independent ionizingdischarge therebetween. With this spacing, any discharges which occurbetween the anodes 9 and Vthe cathanode 'l are directly the result ofelectrons which pass from the gaseous discharge space through theopenings in the cathanode Under these conditions a complete control ofthis discharge can be secured by a potential on the control member 8.

I have found that in a tube of the type described, a certain type ofoperation can be secured wherein the discharge between the cathode 4 andthe cathanode 'l passes with a very low voltage between theseelectrodes, which voltage in some cases may be zero. In `some cases thisdischarge carrying fa current considerably greater in value than a spacecharge limited current passes at these low voltages with no visibledischarge in the cathode-cath-anode space. By visible discharge is meanta discharge which liberates radiations to such an extent that they arereadily visible to the human eye. A discharge which is not thus readilyvisible may be termed a dark discharge.

One circuit in which this type of operation occurs is shown in Fig. 2.In this circuit the heating filament is supplied with heating 'currentby connecting wires 24 and 25 to some suitable source of heating currentnot shown. The control grid 8 and the anode 9 are connected in a highfrequency oscillating circuit by having the wires 38 and 32 connected tothe extended conductors 34 and 35, respectively. A condenser 36 isconnected between the conductors 34 and 35 by the adjustable connections31 and 38. In this way the condenser can be moved along the conductors34 and 35, thereby tuning the oscillating circuit to variousfrequencies. I have found that in a particular instance frequencies oithe order of 108 c. p. s. were suitable. This is about 2.5 meters Wavelength. A suitable source of potential, such as a potentiometer,connected by conducto-rs 48 and 4| across a 550 volt supply line, may beutilized to supply the proper potentials to the tube elements. Thecathode 4 is connected by the conductor 28 to the negative terminal ofthe potentiometer. The cathanode 'l is connected through a highfrequency choke 42 to an adjustable tap 43 on the potentiometer whilethe anode 9 is connected through a high frequency choke 44 to anotheradjustable tap 45 on the potentiometer. 'I'he controlgrid 8 is theconductors 35 and 32 in seres.

, tively high value.

connected through a high frequency choke 46 and an adjustable resistance41 to the conductor 28 of the cathode 4. This resistance is of arelatively low value, for example, ohms or less, whereby `a suitablenegative bias is created on said control grid 8.

When the circuit described above is energized, oscillations are produced in the circuit of the condenser 36, which oscillations may beutilized in any suitable output device 48 coupled to the oscillatingcircuit by means of a coupling coil 49. The coil 49 may be tuned to theoscillator frequency by a condenser 50.

When the tube as shown oscillates, I have found that the voltage dropbetween the cathode 4 and the cathanode 1 falls to a very low value. Ina particular case t-ap 43 was moved so 'that the voltage impressedbetween the cathode 4 and the cathanode 'I was two volts, which is lessthan the ionization voltage of the gases used, and a current ofmilliamperes iiowed between the cathode and cathan-ode. This was not thelimiting value of this current, but was the value determined by theresistance in the potentiometer. Under these conditions, the luminousdischarge disappeared in the cathode-cathanode space, but a faintluminous discharge was observed in the space between the control grid 8and the anode 9.

In accordance with my present understanding of the theory of operationof this device, the

phenomena which are involved are as follows.`

controlled space and come under the incduence` of the control electrode8. The cathanode 1, the control grid 8, and the anode 9 then constitutea triode system, which connected to the oscillating circuit causesoscillations to be generated therein. The chokes 42, 44 and 46 serve tokeep these oscillations out of the portions of the circuit where theyare undesirable. The choke 44 particularly causes the oscillationsproduced to vary the voltage at the anode 9. The resistance 4l keeps thecontrol grid 8 at an average potential relatively close to that of thecathode 4, while the choke 46 causes the oscillations produced to varythe potential of the grid 8 with respect to this average value. Underthese conditions the osc'illating circuit comprises the control grid 8,the anode 9, the conductor 34, the condenser 36, and

The oscillations generated in this circuit periodically cause the anode9 to become highly positive with respect to the control grid 8. Whilethe anode is becoming more positive, at the same time the grid isbecoming more negative so that 'the voltage between these electrodes mayreach a comparaoscillation, however, the anode becomes less positive andthe control grid becomes less negative so that the potentials on theseelectrodes may reach approximately the same value so that substantiallyno potential exists between them.

f The theory of operation further contemplates that the electrons whichenter the controlled discharge space through the openings in thecathanode l, and also through the openings in the control grid 8, comeunder the influence of the positive potential on the anode 9, andproduce some positive ions in the space between the control ele'ctrode 8and the anode 9. This ionization, however, is not of suiicient extent tocompletely neutralize the space charge in the controlled Within the sameperiod of;

spiace so that the control electrode 8 still operates in the propermanner. When the tube is oscillating, as pointed ou-t above, during oneportion of the oscillation cycle, the anode 9 becomes highly positivewith respect to the control grid 8. Under these conditions the positiveions created in the control grid anode space are accelerated toward thecontrol grid 8. AUnder static conditions, substantially all of thesepositive ions would be captured either by the control grid 8 or by thecathanode 1'. However, at the high frequencies which are used, the nighttime of p'ositive ions as they pass from the vicinity of the anode 9 tothe vicinity of the control grid 3 is of the order of magnitude of thetime of a single oscillation period. 'Ihe constants of the circuit andthe spacing between the control grid 8 and the anode 9 are so chosenthat this relationship occurs. In the tube which I used to obtain theresults specified above, the spacing between the cont-rol grid 8 and theanode 9 is about .030 inch. Therefore by the time a positive ion whichis accelerated by the control grid 8 reaches said control grid, thevoltage of that grid will have changed so that it is no longer highlynegative with respect to the anode S. This potential condition permitsthe positive ions, `accelerated as described above, to readily slidethrough the openings in the control grid S. These positive ions,therefore, leave the control grid 8 at a relative-ly high speed, whichmay be of the order of 1000 volts under the conditions which I havespecified. These high speed positive ions also appear to pass readilythrough the openings in the cathanode v1, due probably to the fact thatthe ionization in the cathode-cathanode region permits the field of thecathode to reach through the openings in `the cathanode 1. Under theseconditions, as I have stated, the positive ions pass readily through theopenings in the cathanode 1, and therefore enter the cathode-cathanodespace at a relatively high speed. These positive ions then continueacross the cathode-'cathanode space to the cathode, whereupon theyconstitute a positive ion current to the cathode. In their passagethrough this space, these positive ions substantially entirelyneutralize the spalce charge therein and permit large numbers o-felectrons to pass through this space with substantially no potentialdrop therein. From the above it will be seen that the discharge betweenthe 'cathode 4 and the cathanode 1, which supplies ele-ctrons to thecontrolled discharge space, can occur in accordance with the presentinvention without any substantial expenditure of energy in this space.

Although I have described an oscillating circuit wiah a wave length ofaboult 21/2 meters above, a considerably diffe-rent frequency from thiscan :be used provided the relationships which I have specied still holdtrue. For exlample, in a tube with the same spacing as that used 'in theprevious circuit, I have secured the same results with a wave-length olfabout 251/2 meters. A circuit in which this frequency was used is shownin Fig. 3. In Fig. 3 those elements which are identical with those shownin Fig. 2 are numbered with the same reference numbers. In Fig. 3 theoscillating circuit consists of an adjustable condenser 5I connectedacross the terminals of an induction coil 52. One end of this circuit isconnected through a condenser 53 to the control grid 8. An adjustableleakage resistance 54 is connected across the condenser 53 in order toimpress upon the control a proper bias potential upon the control grid8; The other end of the oscillating circuit is connected through acondenser 55 and a coil 56 consisting of a few turns. The condenser 55prevents the positive potential applied to the anode 9 from also beingapplied to the grid 8. I have found that without the coil 55 certainparasitic oscillation-s were produced While with this coil 56 suchparasitics were prevented from occurring. The desired positive potentialis impressed upon the anode 9 by a conductor 51 connected from 1a pointbetween the condenser 55 and the coil 56 through a high frequency choke5t, and a current-controlling resistance 59 to the adjustable tap 55 onthe potentiometer 39. A coil 5D is coupled to the `oscillating rcoil 52,whereby the output of the oscillator may be led to any suitable outputdevice E l. The cathanode 1 is connected through a high frequency chokeG2 and a current-controlling resistance S3 to the adjustable tap t3.v

When `the circuit described above is energized, oscillations areproduced in the oscillating circuit 5I, 52. At the wave length orfrequency which I hlave described, the same phenomena which occurred inconnection with Fig. 2 likewise occurred in this arrangement, namely,that the cathodecathanode space .became dark while a slight glowappeared in the Acontrol grid anode space, and also a `considerableamount of current owed between the cathode-cathanode under very lowvoltage conditions.

In the particular instance which I have mentioned, I moved ltheadjustable tap 43 so that the cathanode 1 was at the same potential asthe cathode 4. Under these conditions a considerable amount of currentflowed from 'the cathode to the cathanode, which current could be variedsimply by varying the magnitude of the currentcontrolling resistance 53.The potentiometer was further adjusted so that the cathanode 1 was madenegative with respect to the cathode 4. Even with a voltage of -13 voltson the cathanode, current still flowed in the same direction a'spreviously from the cathode to the cathanode, although its magnitude wasconsiderably reduced. Thus it will be seen that in accordance with thisinvention, the drop across the cathode-cathanode space can .be mfadesubstantially zero, and some current will flow even when the cathanodeis negative with respect to the cathode.

Of course it is to lbe understood that this invention is not limited tothe particular detail-s of construction and operation as described aboveas many equivalen-ts will suggest themselves to those skilled in theart. We see lthfat the present invention presents a lmeans wherebycurrent can be conducted Iacross a gaseous dis' charge space at very lowvoltage drop, and consequently very llow loss. Thus this `arrangementcould be utilized in `connection with lampliners, rectifiers, andvarious other types of gaseous discharge devices. In the case of arect-incr, the voltage to be rectied could be impressed directly acrossthe Acathode and cathanode, in which case the ycathanode wouldconstitute the lanode of the rectier system. Likewise various othermethods of producing positive ions and accelerating them into thelcathode-cathanode space for the purpose o-f neutralizing @the spacecharge might be de- 7 What is .claimed is: 1. In'an electrical gaseousdischarge device comprising ian envel-ope ycontaining anelectronemissive cathode, another electrode, a gaseous lling at apressure at which ionization o-f said filling at the applied voltagesmay occur, and means 1for generating positive ions outside of the spacebetween said cathode land additional electrode, the method whichcomprises generating positive ions in said outside space and passingsaid positive ions into said space `in suiiicient numbers and sufoientvelocity to substantially entirelyneutralize therein the negative spacecharge of the electrons emitted from said oathode.

2. `In Ian electrical gaseous discharge device comprising an envelopecontaining an electronemissive cathode, another electrode, a gaseousfilling at a pressure at which ionization o-f said filling at theapplied voltages may occur, and means for generating positive ionsoutside of the space between said cathode and additional electrode, tthemethod which comprises generating positive ions in said outside space:and passing said positive ions into said space in suffi-cient numbersand sufiicient velocity to clause 'a current of electrons to flow fromsaid cathode to said additional electrode at vol-tages bel-ow theionization voltage of said gaseous filling yand without the occurrenceof a visible discharge therein in the `disch-arge space between saidcathode and additional electrode.

3. An electrical gaseous discharge device cornprising an envelopecontaining an electron-emissive cathode, another electrode, a gaseouslling at a pressure at which ionization of said filling at the appliedvoltages may occur, and means for generating positive ions outside ofthe space between said cathode and additional electrode and for passingsaid positive ions into said space, comprising a perforated electrodeand a cooperating electrode spaced therefrom, and means for impressing ahigh frequency potential between them in such a way that the cooperatingelectrode becomes periodically positive with respect to said perforatedelectrode and then substantially less positive with respect to saidperforated electrode, the spacing between said perforated electrode andsaid cooperating electrode being of the order of magnitude such that thetime a positive ion takes to travel between said cooperating electrodesand said perforated electrode is of the order of magnitude of the timeof one cycle of said high frequency potential.

4. An electrical gaseous discharge device cornprising an envelopecontaining an electron-emissive cathode, another electrode, a gaseousfilling at a pressure at which ionization of said filling at the appliedvoltages may occur, and means for generating positive ions outside ofthe space between said cathode and additional electrode and for passingsaid positive ions into said space, comprising a perforated electrodeand a cooperating electrode spaced therefrom, and means for impressing ahigh frequency potential between them in such a way that the cooperatingelectrode becomes periodically positive with respect to said perforatedelectrode and then substantially less positive with respect to saidperforated electrode, the spacing between said perforated electrode andsaid cooperating electrode being of the order of magnitude of the meanfree path of molecules of said gaseous filling, the frequency of saidhigh frequency potential being such that the time of one cycle thereofis of the order of magnitude of the time a positive ion takes to travelbetween said cooperating electrode and said perforated electrode.

5. In an electrical gaseous discharge device comprising an envelopecontaining an electronemissive cathode, a perforated cathanodesurrounding said cathode, a grid surrounding said cathanode, and ananode surrounding said grid, the method which comprises generatingpositive ions in the space between said grid and anode and passing saidpositive ions into the space between said cathode and cathanode insuiicient numbers and sufficient velocity to substantially entirelyneutralize therein the negative space charge of the electrons emittedfrom said cathode by impressing a high frequency potential between saidanode and grid, so that the anode becomes periodically positive withrespect to said grid and then substantially less positive with respectto said grid, said high frequency potential being of such a magnitudeand periodicity to produce said ionization in the space between saidanode and grid.

6. An electrical gaseous discharge device comprising an envelopecontaining an electron emissive cathode, a perforated cathanodesurrounding said cathode, a grid surrounding said cathanode, and ananode surrounding said grid, means for generating positive ions outsideof the space between said cathode and cathanode and for passing saidpositive ions into said space, and means for impressing a high frequencypotential between them in such a way that the anode becomes periodicallypositive with respect to said grid and then substantially less positivewith respect to said grid, the spacing between said grid and said anodebeing of the order of magnitude such that the time a positive ion takesto travel between said anode and said grid is of the order of magnitudeof the time of one cycle of said high frequency potential.

'7. An electrical gaseous discharge device comprising an envelopecontaining an electron emissive cathode, a perforated cathanodesurrounding said cathode, a grid surrounding said cathanode, and ananode surrounding said grid, means for generating positive ions outsideof the space between said cathode and cathanode and for passing saidpositive ions into said space, and means for impressing a high frequencypotential between them in such a way that the anode becomes periodicallypositive with respect to said grid, the spacing between said grid andsaid anode being of the order of magnitude of the mean free path ofmolecules of said gaseous filling, the frequency of said high frequencypotential being such that the time of one cycle thereof is of the orderof magnitude of the time a positive ion takes to travel between saidanod and said grid. l

8. An electrical gaseous discharge device comprising an envelopecontaining an electron-emissive cathode, another electrode, a gaseousfilling at a substantial pressure, means for establishing said otherelectrode at a positive direct current potential with respect to saidcathode in the region from zero to a value substantially less than theionization voltage of said gaseous filling, and means for generatingpositive ions outside of the space between said cathode and otherelectrode and for passing said positive ions into said space insufficient numbers and sufficient velocity to cause a current ofelectrons to flow from said cathode to said electrode at said potentialsubstantially less than the ionization voltage of said gaseous filling.

9. An electrical gaseous discharge device coinprising an envelopecontaining a gaseous filling at a substantial pressure, an electronemissive cathode, a perforated. cathanode spaced from said cathode, agrid adjacent said cathanode, and an anode adjacent said grid, means forestablishing said cathanode at a positive direct current potential withrespect to said cathode in the region from zero to a value substantiallyless than the ionization voltage of said gaseous filling, means forimpressing a high frequency potential between said anode and grid, Iandmeans ior causing a substantial high frequency voltage to appear betweensaid cathanode and cathode comprising a substantial high frequencyimpedance interposed between said cathanode and said cathode.

10. An electrical gaseous discharge device comprising an envelopecontaining a gaseous iilling at a. substantial pressure, an electronemissive cathode, a perforated cathanode surrounding said cathode, agrid surrounding said cathanode, and an anode surrounding said grid,means for establishing said cathanode at a positive direct currentpotential with respect to said cathode in the region from zero to avalue substantially less than the ionization voltage of said gaseousiilling, means for impressing a high frequency potential between saidanode and grid, and means for causing a substantial high frequencyvoltage to appear between said cathanode and cathode comprising asubstantial high frequency impedance interposed between said cathanodeand said cathode.

11. In an electrical gaseous discharge device comprising an envelopecontaining an electronemissive cathode, another electrode, a gaseousfilling in said envelope at a pressure at which ionization of saidfilling at the applied voltages may occur, and means including a voltagesource for producing ionization of said gaseous filling outside of thespace between said cathode and additional electrode and for passingpositive ions from said outside space into said space in sufcientnumbers and suilicient velocity to substantially entirely neutralizetherein the negative space charge of the electrons emitted from saidcathode to the extent that the voltage drop between said cathode andadditional electrode becomes substantially less than the ionizationvoltage of said gaseous filling.

12. In an electrical gaseous discharge device comprising an envelopecontaining an electronemissive cathode, another electrode, a gaseousfilling in said envelope at a pressure at which ionization of said llingat the applied voltages may occur, and means including a voltage sourcefor producing ionization of said gaseous lling outside of the spacebetween said cathode and additional electrode and for passing saidpositive ions from said outside space into said space in sufticientnumbers and sufficient velocity to cause a current of electrons to iiowfrom said cathode to said additional electrode at voltages below theionization voltage of said gaseous filling and without the occurrence ofa visible discharge therein in the discharge space between said cathodeand additional electrode.

13. In an electrical gaseous discharge device comprising an envelopecontaining an electronemissive cathode, a perforated cathanodesurrounding said cathode, a grid surrounding said cathanode, and ananode surrounding said grid, means for impressing a high frequencypotential between said anode and grid to make the anode periodicallypositive with respect to said grid, and then substantially less positivewith respect to said grid, said high frequency potential being of such amagnitude and periodicity to produce ionization in the space betweensaid anode and grid, and to pass positive ions into the space betweensaid cathode and cathanode in suicient numbers and suiiicient velocityto substantially entirely neutralize therein the negative space chargeof the electrons emitted from said cathode.

JAMES D. LE VAN.

